Copper powder can be used in powder metallurgy applications to make sintered products. The copper powder is typically blended with iron or graphite powders, often in combination with alloying powders such as tin. It is then compacted and sintered to make the desired product. While this technology has been used widely for many years, there is a continuing need for higher strength products. A problem with obtaining such higher strength products relates to the fact that the sintering process used to make these products inherently produces products with relatively high concentrations of voids. The present invention offers a solution to this problem by providing copper powders having lower apparent densities than the those currently available. The copper powders of the present invention have apparent densities in the range of about 0.20 to about 0.60 grams per cubic centimeter. Currently available low density copper powders, on the other hand, generally have apparent densities in excess of about 0.65 grams per cubic centimeter and typically in excess of about 0.8 gram per cubic centimeter. The low density copper powders provided by this invention permit a more intimate contacting between the copper powder and the powders (e.g., iron, powders, graphite powders, etc.) they are blended with during compacting and sintering. This more intimate contacting allows for higher strength products having lower void concentrations.
U.S. Pat. Nos. 5,458,746; 5,520,792; and 5,670,033 disclose a process for making copper metal powder from copper-bearing material, comprising: (A) contacting said copper-bearing material with an effective amount of at least one aqueous leaching solution to dissolve copper ions in said leaching solution and form a copper-rich aqueous leach solution; (B) contacting said copper-rich aqueous leaching solution with an effective amount of at least one water-insoluble extractant to transfer copper ions from said copper-rich aqueous leaching solution to said extractant to form a copper-rich extractant and a copper-depleted aqueous leaching solution, said extractant comprising (i) at least one oxime characterized by a hydrocarbon linkage with at least one --OH group and at least one .dbd.NOH group attached to different carbon atoms on said hydrocarbon linkage, (ii) at least one betadiketone, or (iii) at least one ion-exchange resin; (C) separating said copper-rich extractant from said copper-depleted aqueous leaching solution; (D) contacting said copper-rich extractant with an effective amount of at least one aqueous stripping solution to transfer copper ions from said extractant to said stripping solution to form a copper-rich stripping solution and a copper-depleted extractant; (E) separating said copper-rich stripping solution from said copper-depleted extractant to form an electrolyte solution; (F) advancing said electrolyte solution to an electrolytic cell equipped with at least one anode and at least one cathode, and applying an effective amount of voltage across said anode and said cathode to deposit copper metal powder on said cathode; and (G) removing copper metal powder from said cathode.
U.S. Pat. No. 5,516,408 discloses a process for making copper wire directly from a copper-bearing material, comprising: (A) contacting said copper-bearing material with an effective amount of at least one aqueous leaching solution to dissolve copper ions into said leaching solution and form a copper-rich aqueous leaching solution; (B) contacting said copper-rich aqueous leaching solution with an effective amount of at least one water-insoluble extractant to transfer copper ions from said copper-rich aqueous leaching solution to said extractant to form a copper-rich extractant and a copper-depleted aqueous leaching solution; (C) separating said copper-rich extractant from said copper-depleted aqueous leaching solution; (D) contacting said copper-rich extractant with an effective amount of at least one aqueous stripping solution to transfer copper ions from said extractant to said stripping solution to form a copper-rich stripping solution and a copper-depleted extractant; (E) separating said copper-rich stripping solution from said copper-depleted extractant; (F) flowing said copper-rich stripping solution between an anode and a cathode, and applying an effective amount of voltage across said anode and said cathode to deposit copper on said cathode; (G) removing said copper from said cathode; and (H) converting said removed copper from (G) to copper wire at a temperature below the melting point of said copper. In one embodiment the copper that is deposited on the cathode during step (F) is in the form of copper powder, and the process includes (H-1) extruding the copper powder to form copper rod or wire and (H-2) drawing the copper rod or wire to form copper wire with a desired cross-section.
The article by I. D. Enchev et al, "Production of Copper Powder by the Method of Electrolytic Extraction Using a Reversing Current", Poroshkovaya Metallurgiya, No. 9 (141), September, 1974, pp. 95-98, discloses the results of an investigation into the production of copper from electrolytes prepared from lean ore solutions by ion exchange and reversing electrolytic extraction. Electrolyte solutions prepared by leaching ore wastes and subsequent extraction with ABF dissolved in kerosene were used. The article reports the following optimum conditions for the electrolytic extraction of copper powder: reversing current density of 1200 A/m.sup.2, durations of the normal and reversed polarity periods of 5 and 1 minute, respectively; electrolyte acidity and temperature of 100-160 grams per liter and 40-50.degree. C., respectively; copper ion concentration of 10 grams per liter; graphite anodes and titanium cathodes; and powder particle size of 100 microns at a purity of 99.95% copper. The reference also indicates that the electrolyte solution that was tested had a chlorine content of 0.01 gram per liter (10 ppm) and an iron content of 0.90-1.20 gram per liter.